Abstract:
Aeolian deposition in the central North Pacific has been well recognized to originate from arid Asian interior. While there is no doubt about the transport of organic matters along with the mineral dust from the source region, little is known about the nature and changes of the terrestrial organic compounds preserved in the deep sea sediments. In this study, higher plant leaf wax n-alkanes from ODP Site 1208 and Site 886 in the North Pacific since the middle Miocene were analyzed to explore long-term changes in vegetation and climate in the source region. Accumulation rates of leaf wax n-alkanes show an increasing trend, consistent with the documented climatic drying of the Asian interior since the late Miocene. The records of carbon isotopic enrichment factors of C (sub 29) n-alkane relative to atmospheric CO (sub 2) (epsilon (sub C29-CO2) ) show a prominent decrease from approximately 12 to approximately 8 Ma. The average epsilon (sub C29-CO2) value prior to approximately 8 Ma is 0.8 ppm heavier than after approximately 8 Ma. Although almost all values of epsilon (sub C29-CO2) (-25.3 to -21.3 ppm) are well within the range of C (sub 3) plants, adjustment of isotope discrimination by C (sub 3) plants is not considered as the main cause of the observed variations. Instead, changes in relative abundance of C (sub 3) vs. C (sub 4) plants are invoked to interpret the epsilon (sub C29-CO2) records. Higher C (sub 4) contribution (17.7+ or -5.3%) to the local vegetation is inferred for the period prior to approximately 8 Ma, implying a slightly warmer climate in the source region. A marked decline in C (sub 4) plants from approximately 12 to approximately 8 Ma, interpreted as a result of regional temperature drop, coincides with the prominent growth of northern Tibetan Plateau around 8 Ma, along with the global cooling climate. Our results therefore point to apparently close links among plateau uplift, development of drying and cooling climates, and vegetation changes in the Asian interior. Abstract Copyright (2012) Elsevier, B.V.